1. Field of the Invention
The present invention relates to, a flowmeter, and more particularly, to an electromagnetic flowmeter with variable-frequency conductivity-sensing function for a liquid in a tube.
2. Description of Related Art
Conductance refers to the ability of materials to allow currents to flow through. In a solid, the current is transmitted via electrons. In a liquid, the current is transmitted via the movement of cation and anion. Conductivity refers to the ability of materials to transmit the current. The conductivity of a liquid is relevant to the concentration of the dissolved ions. The conductivity meter is a device for measuring the ability of transmitting currents for a liquid.
Traditional conductivity meter often uses a constant current source (micro-ampere class) or a Wheatstone bridge structure for measuring. However, it's easy to be influenced by the noises and ripples in circuit because output current is small. Also, the measuring range is not large enough so that the measuring precision is not stable and not high enough.
Further, the traditional conductivity meter measures the conductivity of a liquid usually via a constant induced current. However, when the conductivity of the liquid is rather low, the induced current for measuring liquids would also decrease. It may result in difficulties when manufacturing the conductivity meter because it is hard to generate induced currents which are small.